Thirty-one percent of Republican voters surveyed by Morning Consult said they are now more likely to vote for Trump, while 20 percent said they are less likely to vote for the real estate mogul. Forty-three percent said Romney's comments had no impact.

Among Trump supporters, 56 percent said they are more likely to vote for Trump after he was denounced by Romney, while 5 percent said they are less likely to vote for Trump. Thirty-six percent said their opinions were not changed.

And among those who voted for Romney, the 2012 GOP nominee, his speech was less helpful in curbing support for Trump: 30 percent were more likely to vote for Trump, while 20 percent were less likely.

Romney ripped Trump as a "fraud" and "phony" during his speech lambasting the real estate tycoon's business record and vision for the country, while Trump criticized Romney as a failed candidate.